Field of the Invention
The present invention relates to a cleaning blade and a process cartridge and an electrophotographic apparatus that include a cleaning blade.
Description of the Related Art
In general, after a toner image formed on a surface (outer circumferential surface) of an electrophotographic photosensitive member (hereafter also simply referred to as a “photosensitive member”) is transferred onto a transfer medium or an intermediate transfer member, or after a toner image is further transferred from an intermediate transfer member onto a transfer medium, a portion of the toner tends to remain on the surface of the photosensitive member and/or the intermediate transfer member. For this reason, the toner remaining on the surface of the photosensitive member or the intermediate transfer member needs to be removed, which is commonly performed with a cleaning blade. This cleaning blade is, for example, a blade-shaped (plate-shaped) article in which the thickness is 1 mm or more and 3 mm or less and a surface facing a cleaning target member (such as a photosensitive member or an intermediate transfer member) has a longitudinal length larger than the thickness.
Such a cleaning blade is used, in an electrophotographic apparatus, in the state of being attached to and fixed by a metal holder, for example. Also, the cleaning blade is disposed such that the edge portion (tip edge-line portion) is in contact with a cleaning target member, for example.
A commonly used material for the cleaning blade is urethane rubber because it is excellent in terms of wear resistance and the degree of permanent set, for example.
In order to meet the recent demand for higher image quality, a toner having a small particle size and a high sphericity (nearly spherical) has been developed. This toner having a small particle size and a high sphericity allows a relatively high transfer efficiency and can meet the demand for higher image quality.
However, the toner having a small particle size and a high sphericity is difficult to sufficiently remove with a cleaning blade from the surface of a cleaning target member, which may result in insufficient cleaning. This is because the toner having a small particle size and a high sphericity tends to slip through small gaps formed between the cleaning blade and the cleaning target member, compared with other toners.
In order to suppress the slipping through of the toner, it is effective to increase the contact pressure between the cleaning blade and the cleaning target member to thereby reduce the gaps.
However, as the contact pressure between the cleaning blade and the cleaning target member increases, the frictional force between the cleaning blade and the cleaning target member tends to increase. As the frictional force between the cleaning blade and the cleaning target member increases, the cleaning blade tends to be pulled in the moving direction of the surface of the cleaning target member, resulting in curling of the edge portion of the cleaning blade is some cases. When the cleaning blade resists the curling force and returns to the original shape, it may make an unusual sound (chatter). When cleaning is performed with such a cleaning blade having a curled edge portion, local wear tends to occur in a region near the edge portion of the cleaning blade (region separated from the edge portion by several to several tens of micrometers). When the cleaning is further performed in this state, the local wear worsens, which results in insufficient removal of the toner during cleaning.
In order to increase the longevity of the cleaning blade and the cleaning target member and to achieve energy conservation, for example, there is a demand for reduction in the rotational torque of the cleaning target member during cleaning (torque reduction). In order to achieve torque reduction, it is effective to decrease the friction between the surface of the contact portion of the cleaning blade and the cleaning target member.
Regarding this torque reduction, Japanese Patent Laid-Open No. 2008-268670 describes a technique of making fine particles having an average particle size of 3 μm or less be present in a surface layer of a cleaning blade formed of urethane rubber (urethane elastomer), the surface layer being in contact with a cleaning target member.
Japanese Patent Laid-Open No. 2012-150203 describes a technique of forming a surface layer in the contact portion (in contact with a cleaning target member) of a cleaning blade, the surface layer having a higher hardness than the base layer of the cleaning blade.
Japanese Patent Laid-Open No. 2009-025451 describes a technique of allowing a continuous increase in the nitrogen concentration of a cleaning blade from the inside of a contact portion (in contact with a cleaning target member) toward the surface of the contact portion.
Japanese Patent Laid-Open No. 2001-075451 describes a technique of making the isocyanurate-group concentration of the surface of an edge portion of a cleaning blade formed of urethane rubber (urethane elastomer) be higher than the isocyanurate-group concentration of the inside of the edge portion.
However, studies by the inventors of the present invention have revealed the presence of the following problems in the above-described existing techniques.
In the bilayer cleaning blade having a surface layer and a base layer such as those described in Japanese Patent Laid-Open Nos. 2008-268670 and 2012-150203, the surface layer and the base layer of the cleaning blade being in contact with a cleaning target member behave differently. For this reason, separation or chipping (hollowing out) of the surface layer is caused in some cases by, for example, irregularities (in general, 1 μm or more and 2 μm or less) of the surface of the cleaning target member or foreign matter (including the toner) present on this surface. When the technique described in Japanese Patent Laid-Open No. 2008-268670 is employed, fine particles tend not to be uniformly distributed in the surface layer, so that considerable variations in characteristics within the contact portion occur, which results in local chipping or insufficient cleaning in some cases.
The technique described in Japanese Patent Laid-Open No. 2009-025451, which is to increase the cross-linking concentration on the surface side of the contact portion (in contact with a cleaning target member) of a cleaning blade formed of urethane rubber (urethane elastomer) to thereby form a hard segment. However, this technique does not allow sufficient torque reduction in some cases.
The technique described in Japanese Patent Laid-Open No. 2001-075451 is to apply a mixed solution of an isocyanate compound and an isocyanurate-forming catalyst to the inner surface of a mold to thereby increase the isocyanurate-group concentration of the surface of a cleaning blade formed of urethane rubber (urethane elastomer). When this technique is employed to increase the isocyanurate-group concentration such that the near-surface portion of the cleaning blade has a substantially uniform hardness and sufficient torque reduction is achieved, the cleaning blade may have a low capability of conforming (conformability) to irregularities in the surface of a cleaning target member or to foreign matter that may be present on this surface. Upon occurrence of degradation of the conformability to irregularities in the surface of a cleaning target member or to foreign matter that may be present on this surface, the above-described slipping through of toner tends to occur.
When toner particles or particles having a size similar to that of toner particles are caught between the cleaning blade and a cleaning target member, the above-described existing techniques tend not to provide sufficiently high conformability to such particles. Specifically, the contact portion (in contact with the cleaning target member) of the cleaning blade deforms with a very large radius of curvature relative to caught particles, so that the toner slips through around the caught particles in some cases.
In addition, within a cleaning blade, different characteristics are required between an image region (developer-coating region) and a non-image region (non-developer-coating region). There is also a problem in which, when a cleaning blade having variations in the hardness distribution is unexpectedly worn in toner-deficient regions such as end portions, a decrease in the hardness and an increase in the coefficient of friction occur.
In particular, end regions in which the supply amount of toner is small tend to wear, resulting in a decrease in the hardness, leading to curling of end portions of the cleaning blade. In conclusion, in order to effectively use a multilayer cleaning blade, curling of end portions in the non-image region needs to be addressed.
The present invention provides a cleaning blade that allows reduction in the friction of the surface of the contact portion in contact with a cleaning target member and that has a high conformability to irregularities in the surface of a cleaning target member and foreign matter that may be present on this surface; a process cartridge including the cleaning blade and an electrophotographic apparatus including the cleaning blade.